Electric coils having serpentine leads



April 2, 1968 o. N. BLOOM v 3,376,536

ELECTRIC COILS HAVING SERPENTINE LEADS Filed Feb. 1]., 1965 INVENTOR OT TO N. B LO OM ATTORNEY 3,376,536 ELECTRIC COILS HAVING SERPENTENE LEADS Otto N. Bloom, 5025 Earle St.,

Rosemead, Calif. 91770 Filed Feb. 11, 1965, Ser. No. 431,851 2 Claims. (Cl. 336-192) This invention relates to electric coils of the small and,

miniature types wherein the winding consists of insulated wire running from about A.W.G. #35 to fine as A.W.G #60, and more particularly the present invention pertains to the leads of coils of the type mentioned, whereby their connection to the winding is not broken during the finishing steps in processing the coil-or during its subsequent installation and service.

There is no set and clear understanding in the trade as to the maximum dimensions of a small or of a miniature coil. My understanding and use of the terms herein is that small coils are those between one-half and one and one-half inches in diameter; and that miniature coils embrace all coils having an outside diameter of less than one-half inch.

Over the past two decades there has been increased demand for and trend toward greater compactness and lightness of automatic apparatus and control devices in general, such as relays, contactors, electro-rnechanical actuators, resonant running devices, etc., and this trend has brought a demand for smaller and lighter electric coils having even greater electrical strength than heretofore. As a result, present specifications for small coils commonly call for A.W.G. #40 wire, and for miniature coils specifications frequently call for A.W.G. #54 wire, or even finer. For manifest reasons it is necessary that coils of the type aforementioned be provided with leads much heavier than the wire of the winding. The diameter of the leads for most coils herein referred to is on the order of that of a coarse human hair. Prior to the present invention these leads have consisted of straight, smooth sections of wire.

Routine inspection tests of small and miniature coils at the production plant has revealed a surprising and perplexing number of initially defective coils; and from the trade came reports of some distressing coil failures during use. My study of the complaints as to coil failures was complicated by the fact that even in carefully removing the Wrapper from a perfect coil, the wrapper removing operation would generally tear the outer lead from the delicate winding. In the end I hit upon the theory that the intially defective coils stemmed from wringing the lead from one or both the terminals ends of the winding during the final manufacturing step of applying the protective wrapperto the coil; and that failures after leaving the plant were mainly due to excessive stresses applied endwise the leads, in either direction, and/or vibrations transmitted along the leads to the juncture of the lead to the winding.

With the-foregoing in find, it is the primary object of the present invention to provide an electric coil in which the aforementioned defects and/or failures are virtually eliminated.

A further object of the present invention is to provide an electric coil including a new and improved lead which eliminates separation of the lead from the end of the winding, and which lead is of such simple construction as will not add appreciably to the cost of manufacture.

Lesser objects of this invention will become apparent 3,376,536 Patented Apr. 2,, 1968 ice fromthe following description and the accompanying drawings.

In general, I accomplish the foregoing objects by providing each coil with a lead or leads each of which is formed adjacent its juncture with the winding into a planar serpentine or zig-zag portion, the terminus of which is connected to an end of the winding. The zig-zag portion prevents rolling of the lead during application of the wrapper to the winding, thus eliminating the former twisting or wringing of the lead from the Winding during application of the wrapper. The zig-zag portion further provides an area to be gripped by several turns of twine and/or the wrapper and thus absorbs endwise stresses applied to the lead, and should such stress or pull on the lead be excessive the zigzag portion may open or stretch without stressing the junction of the lead to the winding. By the same token, vibrations sent along the lead normally are absorbed by the zigzag portion without their reaching the winding at the solder connection.

The invention will now be set forth in detail, the following description to be read in conjunction with the accompanying drawings in which:

FIG. 1 is a greatly enlarged elevation of a coil of the type aforementioned embodying the present invention, a portion of the wrapper being broken away to show the arrangement of a lead in accordance with the present invention.

FIG. 2 is a longitudinal section of the coil of FIG. 1, the length of which is here reduced to save space;

FIG. 3 is a cross-section thereof;

FIG. 4 is a fragmentary detail showing in cross-section the manner the lead is held to the winding;

FIG. 5 is a greatly enlarged view of a lead according to the present invention;

FIG. 6 is a view similar to FIG. 1 wherein the finish or outer lead is according to the present invention and the lead to the start end of the winding is conventional; and

FIG. 7 illustrates the application of the present invention to a self-supporting or bobbinless coil.

Referring now to the drawings in detail, wherein is depicted several commercial embodiments of the present invention and wherein like reference numerals designate like parts in each of the several views, and for the moment referring to FIGS. l-4, 10 designates a bobbin or spool on which a winding 11 of insulated wire is spirally wound. To simplify illustration of other elements, winding 11 is depicted in FIG. 1 in spaced patches, though it is in fact continuous. The bobbin, as is conventional, includes a tubular core 12 and end flanges 13, 14. The bobbin may be of any of the well-known dielectric materials, such as Teflon or Mylar. It is preferred that the bobbin be of exceptionally thin material to thus provide extra space for receiving Winding and its structure preferably should follow the disclosure of my Patent No. 3,159,907 of Dec. 8, 1964. The winding is protected by a snugly fitted covering or wrapper 15 which latter commonly is of the same material as the bobbin. Wrapper 15 is comprised of a spirally wound flexible, strip, with the edges of the several turns overlapping.

Each winding necessarily has two ends, herein designated as the start or inner end 16 and the finish or outer end 17. During the winding operation the tail portion of the start end of the winding is temporarily anchored, for example to the outer wall of its adjacent flange 13 of the bobbin, in order to be readily accessible for connection to its respective lead upon completion of the winding. Like leads 18, .19 are connected to each end of the winding. The leads may be insulated or bare as the needs of the installation may dictate. Each lead is formed adjacent its inner end with a planar serpentine or zig-zag portion 20, the terminus 21 of which portion is soldered at 22 to its respective end of the winding. A patch (or patches) 23 of insulation sheet material (shown in dotted outline in FIG. 1) is disposed under the zig-zag portion of the leads. The patch 23 may be of Teflon or other material of substantially equivalent dielectric strength and preferably is impregnated with glass. The patches perform the multiple purpose of serving as a buffer and insulation between the lead and winding, thus protecting the winding from being scratched and shorted should said zig-zag portion of the lead be stretched, and it also furnishes a larger and firmer anchorage against which to clamp the leads with minimal likelihood of displacement.

Within wrapper a number of turns of yarn or twine 24 extends around the winding, and over the patch and zig-zag portion of the leads to secure both of the last mentioned elements to the winding. The wrapper 15, in 'addition to protecting the winding, also assists in binding the patch and zig-zag portion of the lead to the winding. Thus no stress likely to be applied to the end of a lead can reach its juncture with the winding. For some particular uses of coils, the wrapper alone is sufficient anchorage for the leads and patch. During application of twine 24 the free end portions 25 of the leads are left projecting substantially radially from the winding. The angular disposition of the twine24- as shown in the drawing is merely for the purpose of distinguishing the latter from the turns of the winding.

The spirally wound wrapper encircles the winding, twine, patches and the zig-zag portion of the leads, while the outer terminal or free end portions 25 of the leads emerge from the coil between selected turns of the wrapper, The free end portions 25 of the leads may be disposed toward either end of the coil, whereby the free ends of the leads may be close together or spaced, as desired, and at any point lengthwise and/or circumferentially of the coil.

As to prior coils having a round wire lead or leads, I am of the belief that in applying the wrapper about the winding, the lead had a tendency to roll with the wrapper as the latter is slightly stretched in being applied, and this explains why the round lead twists or wrings off the end of the delicate winding. Therefore, for optimum benefits of the present invention, serpentine portion should extend lengthwise the bobbin in order that said portion 20 may lie flat against the outer surface of the winding. Because of the width of the serpentine portion and the manner it is clamped to the winding, the lead cannot roll during application of the wrapper. Thus the primary cause of defective coils due to factory technique is eliminated.

If during installation of the coil of FIGS. 1-4 in a circuit, some heavy-handed mechanic should pull excessively on the free end of a lead, the relatively large and irregular area provided by the serpentine portion will be apt to withstand the stress; and said serpentine portion may even be stretched before said stress reaches the juncture of the lead and winding. The serpentine lead thus takes care of the second cause of failure of prior coils. This result cannot be accomplished by use of a plain or flat strip as the outer lead.

In use, the coil is sometimes supported by its leads, and in such an arrangement the coil and its leads are often subjected to considerable vibration. In a plain lead, vibration transmits or telegraphs vibratory stresses along the lead to its juncture with the winding, and sometimes the effect is to push or pull the lead endwise along the winding. This action builds up stresses at the juncture of the lead and winding, and where the coil has a plain lead said stresses often cause coil failure. Such stresses appear to have little or no effect on coils incorporating the present invention, inasmuch as the convolutions of the serpentine portion of my lead absorbs such stresses and prevents their reaching the delicate juncture of the lead and winding. Thus my lead eliminates the third cause of failure attributable to leads.

In the modification of FIG. 6 a lead 19 of the present invention is shown in combination with a conventional type start lead 26. In this form of the invention the patch 23 is omitted as illustrative that substantial advantages of the present invention are present in the absence of the patch. Lead 26 is in the form of a copper wire or a fiat strip of like material. This lead extends radially inward along the inner wall of flange 13 to the core of the bobbin, and a portion 27 of same runs along the core to a point 28, where it is soldered to the start end of the winding. The Winding serves to compress portion 27 against the core and thus anchor same. Before wrapper 15 is applied, the exposed end of the lead is bent to provide a portion 29 running parallel with the surface of the winding. After a portion of the wrapper is applied, the free end 30 of the lead is bent outwardly to project between contiguous edges 31 of the turns of the wrapper, Since in the conventional coil the lead to the start end extends well into the body of the coil, this lead is not subject to the objections noted above. However, if the inner lead be attached to the start of the winding at the surface of the winding, it is subject to all the causes of failure noted above.

FIG. 7 is a fragmentary showing of a lead according to the present invention applied to a self-supporting or bobbinless coil, the wrapper being omitted to better portray the present invention. The reference numerals of this figure correspond with those employed in FIGS. 1-4. and a detailed description thereof is deemed unnecessary. In this type of coil the turns of the winding are held fast together as by cement, imparting rigidity to the winding.

While several preferred applications of the present invention have been disclosed, the present teaching will suggest to those skilled in the art further modifications and applications of the concept of the present invention. It is to be understood, therefore, that the scope of the present invention is to be limited only by the terms of the following claims.

What is claimed is:

1. An electric coilcomprising a cylindrical winding of fine gauge insulated wire, a pair of leads connected to the ends of the winding at opposite ends of the coil, each lead being substantially larger in diameter than the wire of said winding and formed between its ends in a substantially flat, serpentine portion extending longitudinally along and conforming substantially to the outer surface of said winding, a strip of insulating material underlying each serpentine portion, a covering wrapping formed of a strip wound about said winding and said serpentine portions, the free ends of said leads extending outwardly through said Wrapping, the wrapping wound about said serpentine portion and insulating strips securing said leads to said coil while said serpentine portions prevent displacement of said leads during winding of said wrapping and said leads are rigidly fixed to said coil against displacement and to form supports for said coil.

2. An electric coil comprising a cylindrical winding of fine gauge insulated wire, a pair of leads connected to the ends of said winding at opposite ends of the coil, each lead being substantially larger in diameter than the wire of said winding and formed between its ends in a substantially fiat, serpentine portion extending longitudinally along and conforming substantially to the outer surface of said winding, a strip of insulating material underlying each serpentine portion, windings of filamentary material extending about said coil and said serpentine portions, to fasten said leads securely to said coil, a covering wrapping formed of a strip wound about said winding and ,said serpentine portions, the free ends of said leads extending outwardly through said wrapping, the wrapping Wound about said serpentine portions and insulating strips secur- 6 ing said leads to said coil while said serpentine portions 2,869,089 1/ 1959 Hampel 336192 prevent displacement of said leads during winding of said 2,929,132 3/1960 Wohlhieter 336-192 X wrapping and said filamentary material and said leads are 3,159,907 12/ 1964 Bloom 336-198 X rigidly fixed to said coil against displacement and to FOREIGN PATENTS form su orts for said coil. 7

pp 0 385,721 1/1933 Great Britain.

UNITED STATES PATENTS DARRELL L. CLAY, Primary Exantiner.

X L- E L. H. Examllters. 2,779,928 1/1957 Jeflrey 336192 10 T. J. KOZMA, Assistant Examiner.

References Cited 

1. AN ELECTRIC COIL COMPRISING A CYLINDRICAL WINDING OF FINE GAUGE INSULATED WIRE, A PAIR OF LEADS CONNECTED TO THE ENDS OF THE WINDING AT OPPOSITE ENDS OF THE COIL, EACH LEAD BEING SUBSTANTIALLY LARGER IN DIAMETER THAN THE WIRE OF SAID WINDING AND FORMED BETWEEN ITS ENDS IN A SUBSTANTIALLY FLAT, SERPENTINE PORTION EXTENDING LONGITUDINALLY ALONG AND CONFORMING SUBSTANTIALLY TO THE OUTER SURFACE OF SAID WINDING, A STRIP OF INSULATING MATERIAL UNDERLYING EACH SERPENTINE PORTION, A COVERING WRAPPING FORMED OF A STRIP WOUND ABOUT SAID WINDING AND SAID SERPENTINE PORTIONS, THE FREE ENDS OF SAID LEADS EXTENDING OUTWARDLY THROUGH SAID WRAPPING, THE WRAPPING WOUND ABOUT SAID SERPENTINE PORTION AND INSULATING STRIPS SECURING SAID LEADS TO SAID COIL WHILE SAID SERPENTINE PORTIONS PREVENT DISPLACEMENT OF SAID LEADS DURING WINDING OF SAID WRAPPING AND SAID LEADS ARE RIGIDLY FIXED TO SAID COIL AGAINST DISPLACEMENT AND TO FORM SUPPORTS FOR SAID COIL. 